The prior art is generally cognizant of machines for size grading pod vegetables having horizontal, rotating drums in which the vegetables are tumbled, the drums having slits or windows out of which pods that are sufficiently small may fall. Various techniques are used to bring these windows or slits to a preselected grading size as they pass under the mass of vegetables and then to an open, clearing position as the windows or slits reach the top of the drum. The clearing position is useful in releasing pods caught in the slits because the pods have proved too large to pass entirely through them.
Examples of size graders in which the windows or slits have a circumferential orientation substantially transverse to the axis of the drum are shown in Urschel, U.S. Pat. No. 1,295,642, and Ryder, U.S. Pat. No. 1,689,254. Devices in which a series of long, grading slits extend the length of the drum, substantially parallel to the longitudinal axis thereof are seen in Holloway, U.S. Pat. No. 3,831,752, and Grosbety, U.S. Pat. No. 3,241,667.
The maintenance of accuracy of slit width is a common problem in size graders having longitudinal slits, owing to the unsupported length of the members used to establish the size of the slits. Such members are vulnerable to bending and subsequent misalignment. Prior art size graders having circumferentially disposed slits or windows substantially transverse to the longitudinal axis of the drum employ intermeshed inner and outer drums of different diameters. Intermeshed drums present problems concerning wear and misalignment that are referred to in Ryder, U.S. Pat. No. 1,689,254, together with problems of adjustment of the grading openings.